The present invention relates generally to agricultural machinery and, more particularly to improvements to self-propelled agricultural machines or to machines which tow or carry implements that are driven via at least one power take-off.
Agricultural machines of this kind generally have a drive engine whose drive power is branched to the main drive and at least one power take-off for driving the implements. At least one measuring device directly or indirectly determines the power transmitted to a power take-off and, in case of overload, generates a control signal for a power regulator for regulating the output power of the drive engine.
Self-propelled working machines of this kind include, for example, agricultural machines, such as combine harvesters, field choppers or tractors, and also construction machinery.
For example, a self-propelled combine harvester has a mechanical or hydrostatic drive arranged behind the drive engine, from which the drive power is transmitted to the drive wheels. A plurality of implements (cutter bar, threshing and separating members, straw chopper, blower, elevator, etc.), are driven apart from the main drive. These implements are driven directly or indirectly as power take-offs by the engine shaft of the drive engine.
With a self-propelled field chopper, the power take-offs function as a means for driving an attachment, the chopper unit, the ejection accelerator and other implements. These implements are operated sometimes parallel and adjacent each other, and sometimes in tandem, one behind the other in a drive train.
With tractors it is known that in addition to the main drive and the hydraulic pumps a power take-off (pto) shaft can be provided for driving additional implements. For cost reasons it is advantageous to drive as many additional implements as possible by means of the drive engine of the tractor. This has led to many tractors having two power take-off shafts (one rear power take-off shaft and one front power take-off shaft). With some tractors there is an additional power take-off shaft at the top for transmitting the drive engine power to additional implements in the upper body region of the tractor.
To satisfy the power requirements of these self-propelled working machines for the main drive and the power take-offs, an increasing output power of the drive engine is necessary. However, due to design limitations, the individual implements and the transmission for the main drive may be operated only up to a maximum input power or torque. Therefore, in certain working situations the drive engine generates a higher torque than can be accommodated by the power take-offs or the transmission, thereby damaging or increasing wear of the drive elements, implements or transmission.
This problem is addressed in German Patent 196 24 085 A1. There, a self-propelled working machine in the form of a cement truck is described which, in addition to the main drive, has a cement mixer driven by the drive engine via the power take-off. The main drive for the cement truck requires a drive engine which is capable of developing torques significantly greater than the maximum permitted torque for the cement mixer. In a cement truck there are basically two working situations: a) road travel of the cement truck with simultaneous driving of the cement mixer; or b) stationary operation of the cement truck with the cement mixer being driven. In working situation b), where the torque of the drive engine is allocated solely to the cement mixer, it is possible for the maximum permitted torque for the cement mixer to be exceeded. For this reason, in working situation b), German Patent 196 24 085 A1 proposes a power regulator to automatically limit the torque of the drive engine when the maximum permitted torque of the cement mixer is reached. However, so that automatic torque limiting can take place, the operator must first activate this limit control by an on/off switch. Furthermore, the overload protection is designed only to protect the cement mixer during stationary operation while the main drive is at a standstill and does not protect the main drive. Beyond the simple function of protecting the cement mixer, the proposed torque monitoring allows no further control over the drive engine.
With the above-mentioned agricultural machines the problem is more complex because i) in addition to the main drive, there are several power take-offs with a larger number of implements; ii) the number of working situations is greater than in the case of the cement truck according to German Patent 196 24 085 A1; and iii) each working situation has different torque requirements for the power take-offs and the main drive. To regulate the drive engine it is desirable not only to protect a single implement against overload by reducing the engine power, but also to regulate the drive engine in such a way that maximum power is available for the working functions of the self-propelled working machine without any of the implements being overloaded in their function.
Different working situations for a combine harvester and a constantly changing load situation of the individual implements arise, for example, when driving in standing crops with different density, when harvesting on hilly land, when harvesting in different soil conditions, when travelling on a road, etc. Frequent changes between different working situations are not uncommon. Moreover the change between different working situations can be made in small steps or quite suddenly.
In a tractor with several power take-off shafts, an important operational factor is which of the attachments are connected. Also, it is significant whether two or even three power take-off shafts are operated simultaneously. Therefore, a large number of permutations of working situations are possible.
It is an object of the present invention to overcome one or more of the problems described above.
Another object of the invention is to further develop a working machine in such a way that optimum operation in different working situations is made possible in a reliable and user-friendly manner, without overloading individual power take-offs or the main drive.